A top drive can be used in a drilling rig for handling a pipe string during drilling or lining a wellbore. In some well operations, an engaging apparatus, including an internal or external pipe gripping mechanism, can be connected below the top drive to grip a joint of pipe, such as casing, so that the engaging apparatus and the joint of pipe can be driven axially and/or rotationally by the top drive. Some engaging apparatus for casing pipe are described in U.S. Pat. No. 6,311,792, issued November 2001 and International application WO00/05483, published February 2000, both to TESCO Corporation.
In a drilling rig, the top drive can be hung in the mast with the engaging apparatus connected in drive communication and in substantial axial alignment therebelow. The top drive and engaging apparatus are hung in the mast above the well center, the top drive and engaging apparatus define a main axis of the drilling rig that is aligned with well center. Joints of pipe, for connection into the drill or liner string, can be supported, for example in a V-door, adjacent the main axis of the drilling rig. For connection into the drill or liner string, the pipe joints can be engaged by an elevator and brought under the drive system for engagement and handling. Generally, the elevator is supported on link arms.
To pick up a pipe joint, the top drive is lowered to permit the elevator, either on conventional link arms or with the cables attached to the link arms, to be manually moved over and engaged about a pipe joint on the V-door. The top drive is then hoisted to pull the pipe joint off the V-door. Once free of the V-door, the pipe joint can be swung by gravity under the engaging apparatus so that the gripping mechanism can engage the pipe joint.
Recently, as described in applicant's U.S. application 2005-009835, published May 12, 2005, a pipe handling device has been introduced wherein the link arms are mounted to move with the top drive but are mounted below the quill of the top drive such that the link arms can be reduced in length and may be closer to the point of implementation over previous systems. In such assemblies of a pipe handling device with a pipe engaging apparatus, the pipe engaging apparatus includes a pipe gripping mechanism that is selected to grip a pipe for rotation thereof, as driven by a top drive and the pipe handling device includes at least one link arm that are, in normal operation, isolated from such rotation in order to hold and position a pipe for gripping by the pipe gripping mechanism, but not itself be rotated. Although the link arm of the pipe handling device is mounted on the pipe engaging apparatus, a bearing is positioned between the link arms and the pipe gripping mechanism to permit rotational isolation of the link arms from the rotation of the pipe gripping mechanism. The bearing can be provided at various points between the pipe gripping mechanism and the at least one link arm depending on the parts of the pipe engaging apparatus that are connected for rotation with the pipe gripping mechanism and top drive.
For example, in one embodiment, with reference to prior art FIG. 1, a pipe handling device 10 may be provided for mounting onto a pipe engaging apparatus 12. The pipe engaging apparatus may include a main housing 14, a mandrel 16 and a pipe gripping mechanism 17 selected to grip a pipe, for example pipe 22 in the Figure. The apparatus is connectable to a top drive 20, for example through an upper end 18 of mandrel 16 and the top drive provides axial and rotational drive for the pipe gripping mechanism and mandrel of the apparatus, which in turn transmits this rotational and axial movement to a pipe being gripped. In this illustrated embodiment, pipe gripping mechanism 17 and mandrel 16 rotate within a main housing 14 as facilitated by a pipe engaging apparatus bearing 32. Main housing 14 in this embodiment generally is maintained stationary relative to the rotating mechanism 17 and mandrel 16 by use of an anti-rotation bracket 21 installed between top drive 20 and housing 14.
The pipe handling device 10 includes at least one link arm 24 having a first end 25 supported on the pipe engaging apparatus and able to pivotally move thereon and an outboard end 27 pivotally connectable to a pipe elevator segment 30, the link arm being sized to present pipe 22 into a position to be gripped by the pipe engaging apparatus. In the illustrated embodiment, link arm 24 is mounted onto main housing 14 of apparatus 12 through a link hanger 29 formed on a link carrier bracket 31. Link hanger 29 forms a shaft on which link arm 24 can pivot. In this way, link carrier bracket and therefore link arm are moved with the main housing and isolated from rotation with the pipe gripping mechanism by bearing 32 and anti-rotation bracket 21.
Although isolated therefrom by bearing 32, the pipe handling device is located in the rotational drive path of the top drive. Thus, in the event that engaging apparatus bearing 32 should fail and seize, link carrier bracket 19 and link arm 24 have the potential to rotate with the top drive. While anti-rotation bracket 21 is intended to resist rotation of the housing 14, link carrier bracket 19 and the link arm, a seized condition of bearing 32 may cause bracket 21 to also fail, as by breaking or ripping away from its installed position, such that the link arm may begin to rotate as driven by the top drive. Although the top drive would be shut down in this situation, such a situation of uncontrolled rotation of the link arms with the top drive could create significant safety concerns.